However, the holding midfielder, who has won 24 caps for his country, does not feel that he can help Slovenia when they take on Slovakia and England in their upcoming World Cup qualifiers.

"The work load is just too high. I've played nine games in a short period of time, and I have caught an infection two weeks ago. I realised that I need to take care of me and my body," Kampl told Rheinische Post after withdrawing from the Slovenia squad.

"It's my decision, and many might fear to make that call because they fear consequences. They just continue, but maybe sustain an injury in end. It's clear that not everyone will understand me."

Germany-born Kampl maintained that his decision is not one against Slovenia, but added that "it's no use to travel there when realise that I won't be able to help."

Slovenia began their World Cup qualifying campaign with a 2-2 draw at Lithuania a month ago, and over the next week host Slovakia and England at the Sportni Park Stozcie in Ljubljana.

Speaking to reporters, national team coach Srecko Katanec said that he was not happy with Kampl's decision and left the Leverkusen player's Slovenia future open.

"Kevin wrote [to] me [saying] that he's exhausted, but I hear that he's training in Leverkusen. He can do whatever he wants," Katanec said. "But I don't know what that means for his national team future. We will see."

Stephan Uersfeld is the Germany correspondent for ESPN FC. Follow him on Twitter @uersfeld.